Anti-lock brakes

Since its 1960s debut, ABS has been keeping drivers in control

Feature Article from Hemmings Motor News

Anti-lock brake systems have detractors among the pump-the-pedal-yourself crowd, even though in test after test, ABS has proven its worth in delivering shorter stopping distances as well as improvements in a driver's ability to maneuver during panic stops. Still, critics contend that there's no conclusive evidence showing that anti-lock brakes have actually played a significant role in reducing traffic accidents. Or to put it another way, it can't make people better drivers.

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Nevertheless, ABS is here to stay, as you're probably aware if you've shopped for a new car or truck lately. But did you know that ABS has been around for nearly a half century?
The system was first developed for fighter planes to prevent landing gear wheels from locking up and skidding on runways and aircraft carrier flight decks. In the 1960s, the Dunlop Maxaret system appeared on the ultra high-performance Jensen Interceptor FF--FF stands for Ferguson Formula, the name for the four-wheel-drive system that the cars were equipped with. The Maxaret ABS relied on the car's center differential to tell it whether the wheels were sliding or not, and then altered the vacuum at the booster to compensate.
The system received mixed reviews, probably in part because it lacked the ability to modulate each wheel individually.
The biggest advancement toward modern ABS came in the early 1970s when Bosch and Mercedes-Benz conspired to put an end to lockups forever with an electronic system that put rotational sensors at each wheel linked to a crude computer that could compare wheel speeds and modulate brake pressure to the ones in danger of locking.
The system first appeared in 1978 on the Mercedes S-Class, and became standard on all Mercedes-Benz automobiles in 1992.
Today, ABS setups are all quite similar, though there are differences in the types of sensors used at the wheel. Many use tone wheels (small wheels with an array of teeth) mounted to the ends of the axles, while some more modern systems use electromagnets inside the axle housing.
The most important aspect of ABS is that it allows the driver to remain in control during a panic stop by allowing him to steer away from an obstacle, and by preventing brake slides that can lengthen stopping distances.

This article originally appeared in the January, 2008 issue of Hemmings Motor News.